Carrier frequency handling in clusters

ABSTRACT

There is provided mechanisms for carrier frequency handling in a cluster based communications network. According to one aspect there is provided a method performed by a wireless device camping on or served by a cluster head device associated with a cluster head carrier frequency. According to one aspect there is provided a method performed by a cluster head device associated with a cluster head carrier frequency. A corresponding wireless device, a corresponding cluster head device, and corresponding computer programs and computer program products are also provided.

TECHNICAL FIELD

Embodiments presented herein relate to cluster based communicationsnetworks, and particularly to methods, devices, a computer programs, andcomputer program products for carrier frequency handling in clusterbased communications networks.

BACKGROUND

In mobile communication networks, there is always a challenge to obtaingood performance and capacity for a given communications protocol, itsparameters and the physical environment in which the mobilecommunication network is deployed.

In national security and public safety (NSPS) scenarios, there is a needto allow wireless devices (such as cellular user equipment, UE, modems,smartphones, sensors, tablet computer, machine type devices) tocommunicate directly with one another when they are under cellularnetwork coverage. In 3GPP LTE networks (NW), this so called Device toDevice communication (D2D) or Proximity Services (ProSe) is madepossible by the “LTE Direct” technology that allows a cellular basestation (BS or eNB) to set up a direct D2D link between two UEs andallocate resources for that link.

D2D communication exists in several versions today. Examples includeBluetooth, several variants of the IEEE 802.11 standards suite such asWiFi Direct, and Flashlinq. Recently, device-to-device communications asan underlay to cellular networks have been proposed as a means to takeadvantage of the proximity of communicating devices and at the same timeto allow devices to operate in a controlled interference environment. Anadvantage with D2D under cellular a cellular NW control (networkassisted D2D) is that optimized spectrum usage as well as low powerdiscovery algorithms can be developed.

A technical mechanism that addresses D2D communication both in andoutside NW coverage is based on clustering, where some of the devices(UEs) act as a Cluster Head (CH) device and other devices act as Slavedevices. A CH device can be compared to a small range base station that,in the absence of a cellular eNB, provides (a subset of and) similarfunctionality as an eNB. For example, a CH device may providesynchronization and radio resource management within the cluster and mayalso act as a central node to create a tree topology for communicationwith the cluster. In addition, the CH device may also provide a relayingfunctionality towards other clusters or towards a cellular eNB.

In a cluster scenario, wireless devices within the cluster are requiredto do cell search on regular basis in order to be able to detect whetherthe wireless device has come into NW coverage again. Once a wirelessdevice (or the CH device itself) determines presence of a regularnetwork node, the cluster has an operative connection to the corenetwork (and Internet Protocol network) and more services may be able tobe supported within the cluster.

In general terms, CH devices are low power nodes, often battery driven,and assumed to have lower cost compared to eNBs (or other regular NWnodes). Therefore, the CH devices will be made up by simpler componentswith lower performance compared to that of an eNB. One such component isthe crystal oscillator (XO), which is used for generating referencetiming and reference carrier frequency. Current NW nodes have a veryaccurate XO and are assumed always to be connected to a power supply(such as a regular power supply, solar power, a powerful battery backup,etc.). The requirement for the frequency accuracy for a NW node is 0.1ppm, corresponding to a frequency error of less than 200 Hz at a carrierfrequency of 2 GHz.

In current wireless devices (mobile phones, tablets, etc.) the XOaccuracy is 10-15 ppm implying a frequency error of ±20-30 kHz at 2 GHz.Hence, once a wireless device at start up connects to a NW node, thewireless today needs need to not only to find a NW node (a cell) to campon but also to find the correct carrier frequency and lock its intervalfrequency generation to a more accurate source than the internal XO ofthe wireless device. Known Cell Search (CS) algorithms aim fordetermination of specific synchronization signals transmitted from theNW nodes in order to determine timing, the exact carrier frequency, aswell as the NW node cell ID. Synchronization signals (PSS/SSS in LTE,P-SCH/S-SCH in WCDMA) used for determining cells in current cellularsystems like LTE and WCDMA/HSPA work with a frequency error of up toapproximately 3-4 kHz. With this robustness of CS, a wireless device canperform CS using its own carrier frequency in connected mode (i.e. whenin-sync with the NW), also for the highest reasonable Doppler shift.However, during initial CS, i.e. when a wireless device has not yetconnected to any NW node, a frequency grid for the CS is needed with a5-10 kHz carrier spacing in order to cope with the uncertainty of theXO.

CH devices may have XOs with accuracies closer to today's UEs thantoday's NW nodes, mainly due to cost and power consumption reasons. Thismeans that the devices in the network need to operate with regularnetwork nodes (such as eNBs) and low power network nodes (such as CHdevices) that have different XO accuracy.

Hence, there is still a need for an improved carrier frequency handlingin heterogeneous communications networks, such as cluster basedcommunications networks.

SUMMARY

An object of embodiments herein is to provide improved carrier frequencyhandling in heterogeneous communications networks, such as cluster basedcommunications networks.

CH devices in out-of-network coverage scenarios act as a synchronizationreference with respect to timing and carrier frequency within thecluster. That means that wireless devices in the cluster adjust theirinternal clocks (XO) to the clock of the CH device. However, since theCH clock reference may be rather inaccurate compared to the truereference (as provided by NW nodes), wireless devices operativelyconnected to the CH devices may experience significant frequency error(larger than 3-4 kHz) when detecting a regular network node. Theinventors of the enclosed embodiments have through a combination ofpractical experimentation and theoretical derivation therefore realizedthat when the wireless device receives information from the CH device,the received information may interfere with information transmittedwithin the network node coverage area. Even if the CH device is assumedto use frequency resources which are orthogonal to the frequencyresources of the network node, adjacent sub-carriers (some transmittedfrom the CH device and some from the network node) will, due to thelarge frequency offset, collide and interfere with each other. This mayharm the capacity in the communications network and make it difficultfor the wireless device to act as a relay between the network node andthe CH device (e.g., for improved service support within the cluster).

An object of embodiments herein is to provide improved carrier frequencyhandling in heterogeneous communications networks, such as cluster basedcommunications networks, by addressing frequency differences betweennetwork nodes and CH devices once at least one wireless device in acluster outside network coverage enters into network coverage again.

According to a first aspect there is presented a method for carrierfrequency handling in a cluster based communications network. The methodis performed by a wireless device. The wireless device is camping on orserved by a cluster head device associated with a cluster head carrierfrequency f_(CH). The method comprises detecting a network node. Thenetwork node is associated with a network node carrier frequency f_(NN).The method comprises, in a case the cluster head carrier frequencydiffers more than a predetermined threshold Δ from the network nodecarrier frequency, reporting an event relating thereto to the clusterhead device.

According to a second aspect there is presented a method for carrierfrequency handling in a cluster based communications network. The methodis performed by a cluster head device. The cluster head device isassociated with a cluster head carrier frequency f_(CH). The methodcomprises acquiring a difference between the cluster head carrierfrequency and a network node carrier frequency f_(NN) associated with anetwork node. The method comprises determining, for a wireless devicecamping on or served by the cluster head device, a frequency adjustmentaction out of at least two possible frequency adjustment actions basedon the magnitude of the frequency difference.

Advantageously the methods of the first and second aspects resolve, orat least mitigate issues relating to large frequency difference betweennetwork nodes and CH devices once at least one wireless device in acluster outside network coverage enters into network coverage again.This may result in less interference in the communications network aswell as ease of relaying information form the network node to thecluster.

According to a third aspect there is presented a wireless device forcarrier frequency handling in a cluster based communications network.The wireless device is arranged for camping on or being or served by acluster head device. The cluster head device is associated with acluster head carrier frequency f_(CH). The wireless device comprises aprocessing unit. The processing unit is arranged to detect a networknode. The network node is associated with a network node carrierfrequency f_(NN). The processing unit is arranged to, in a case thecluster head carrier frequency differs more than a predeterminedthreshold Δ from the network node carrier frequency, report an eventrelating thereto to the cluster head device.

According to a fourth aspect there is presented a cluster head devicefor carrier frequency handling in a cluster based communicationsnetwork. The cluster head device is associated with a cluster headcarrier frequency f_(CH). The cluster head device comprises a processingunit. The processing unit is arranged to acquire a difference betweenthe cluster head carrier frequency and a network node carrier frequencyf_(NN) associated with a network node. The processing unit is arrangedto determine, for a wireless device camping on or served by the clusterhead device, a frequency adjustment action out of at least two possiblefrequency adjustment actions based on the magnitude of the frequencydifference.

According to a fifth aspect there is presented a computer program forcarrier frequency handling in a cluster based communications network,the computer program comprising computer program code which, when run ona wireless device, causes the wireless device to perform a methodaccording to the first aspect.

According to a sixth aspect there is presented a computer program forcarrier frequency handling in a cluster based communications network,the computer program comprising computer program code which, when run ona cluster head device, causes the cluster head device to perform amethod according to the second aspect.

According to a seventh aspect there is presented a computer programproduct comprising a computer program according to at least one of thefifth and sixth aspect, respectively, and a computer readable means onwhich the computer program is stored.

It is to be noted that any feature of the first, second, third, fourth,fifth, sixth and seventh aspects may be applied to any other aspect,wherever appropriate. Likewise, any advantage of the first aspect mayequally apply to the second, third, fourth, fifth, sixth, and/or seventhaspect, respectively, and vice versa. Other objectives, features andadvantages of the enclosed embodiments will be apparent from thefollowing detailed disclosure, from the attached dependent claims aswell as from the drawings.

Generally, all terms used in the claims are to be interpreted accordingto their ordinary meaning in the technical field, unless explicitlydefined otherwise herein. All references to “a/an/the element,apparatus, component, means, step, etc.” are to be interpreted openly asreferring to at least one instance of the element, apparatus, component,means, step, etc., unless explicitly stated otherwise. The steps of anymethod disclosed herein do not have to be performed in the exact orderdisclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concept is now described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating a cellular communicationnetwork according to embodiments;

FIG. 2a is a schematic diagram showing functional modules of a wirelessdevice according to an embodiment;

FIG. 2b is a schematic diagram showing functional units of a wirelessdevice according to an embodiment;

FIG. 3a is a schematic diagram showing functional modules of a clusterhead device according to an embodiment;

FIG. 3b is a schematic diagram showing functional units of a clusterhead device according to an embodiment;

FIG. 4 shows one example of a computer program product comprisingcomputer readable means according to an embodiment; and

FIGS. 5, 6, 7, and 8 are flowcharts of methods according to embodiments.

DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter withreference to the accompanying drawings, in which certain embodiments ofthe inventive concept are shown. This inventive concept may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided by way of example so that this disclosure will be thorough andcomplete, and will fully convey the scope of the inventive concept tothose skilled in the art. Like numbers refer to like elements throughoutthe description. Any feature or step indicated by dashed lines should beregarded as optional.

FIG. 1 shows a schematic overview of an exemplifying cellularcommunication network 11. The cellular communication network 11comprises a network node (NN) 14 providing network coverage over a cell15. A cell 15 is served by at least one of network node 14. A wirelessdevice (WD) positioned in a particular cell is thus provided networkservice by the network node 14 serving that particular cell 15. Further,the network node 14 is arranged to communicate with other network nodes(not shown) via communications links. The network node 14 is alsooperatively connected to a core network 16. The core network 16 mayprovide services and data to the WD operatively connected to at leastone network node 14 from an external packet switched Internet Protocol(IP) data network 17. The cellular communications network 11 maygenerally comply with any one or a combination of W-CDMA (Wideband CodeDivision Multiplex), LTE (Long Term Evolution), EDGE (Enhanced DataRates for GSM Evolution, Enhanced GPRS (General Packet Radio Service)),CDMA2000 (Code Division Multiple Access 2000), WiFi, microwave radiolinks, HSPA (High Speed Packet Access), etc., as long as the principlesdescribed hereinafter are applicable.

One situation that could arise is that one or more of the WDs (such asWDs 13 a, 13 b) are outside the coverage area 15 of the network node 14,or that there is a failure of the network node 14 or that the maximumcell load limit of a network node 14 is reached. In order for a WD 13 a,13 b not able to establish a direct communications link to a networknode 14 to access services and data of the IP data network 17, or for aWD 13 a, 13 b to engage in local communications with UEs that are in itsproximity (for this or any other purpose), clustering mechanisms may bedeployed in the communications network 1 a. By means of the clusteringmechanisms an ad hoc network may thus be formed. Such mixed cellular andad hoc networks provide a natural solution to providing communicationservices with partial infrastructure coverage or even in geographicalareas without any cellular network coverage due to lack ofinfrastructure or due to natural disaster, public safety or failuresituations. The cellular communication network 11 therefore furthercomprises cluster head (CH) devices 12 a, 12 b. The CH devices 12 a, 12b may be regarded as low power nodes. Physically, the CH devices 12 a,12 b may be of the same type as the WDs 13 a, 13 b. The CH devices 12 a,12 b are arranged to serve as low power network nodes. The term CHdevice is thus used herein to distinguish the role a device, such as aUE, takes in a cluster context. The CH devices 12 a, 12 b may in otheraspects be identical to the wireless devices 13 a, 13 b. As the skilledperson understands, the cellular communications network 11 may comprisea plurality of network nodes 14 and a plurality of WDs 13 a, 13 b and CHdevices 12 a, 12 b operatively connected to at least one of theplurality of network nodes 14.

In the cellular communication network 11 it is assumed that the networknode 14 is power supplied (regular power supply, solar power, batterybackup etc.) and is using high cost components. Hence its crystaloscillator (XO) is assumed to be very accurate and the network node 14therefore also assumed to transmit with a correct carrier frequency,f_(c)=f₀. Two different clusters are shown in FIG. 1; a first clustercomprises wireless device 13 a operatively connected to cluster headdevice 12 a, and a second cluster comprises wireless device 13 boperatively connected to cluster head device 12 b.

For the first cluster the cluster head device 12 b is within thecoverage of the network node 14 (as defined by the cell 15). In thiscase, the network node 14 serves as the reference clock (and as thecarrier frequency reference), and the cluster head device 12 a servingthe wireless device 13 a outside of the network coverage may thus be insynchronization with the network node 14 via the cluster head device 12a. The wireless device 13 a is therefore assumed to transmit on thecorrect carrier frequency f_(o).

For the second cluster, both the wireless device 13 b and the clusterhead device 12 b are outside the coverage of the network node 14 (asdefined by the cell 15). In this case the cluster head device 12 bserves as the clock reference. However, due to an inaccurate XO in thecluster head device 12 b (as compared to the XO of the network node 14)there may be a large frequency error in the carrier frequency, i.e.f_(c)=f_(o)+Δ. In this case, the wireless devices served by the clusterhead device 12 b may, as will be further disclosed with references tothe enclosed embodiments, configured with information about possiblefrequency error, due to the inaccurate clock in the cluster head device12 b. As will be further disclosed with references to the enclosedembodiments, once a wireless device (or the CH device itself) determinespresence of a network node 14 from performing a cell search, itdetermines the carrier frequency of the network node 14 relative thecarrier frequency of the CH device. If the difference is larger than apredetermined value (hereinafter denoted A) a “frequency event” isreported to the CH device. The CH receives the information and updatesits carrier frequency, and may also in some embodiments inform wirelessdevices operatively connected to the CH device.

The embodiments disclosed herein thus relate to carrier frequencyhandling in a cluster based communications network 11. In order tofacilitate carrier frequency handling in a cluster based communicationsnetwork 11 there is provided a wireless device 13 a, 13 b a methodperformed by the wireless device 13 a, 13 b, a computer programcomprising code, for example in the form of a computer program product,that when run on a wireless device 13 a, 13 b, causes the wirelessdevice 13 a, 13 b to perform the method. In order to facilitate carrierfrequency handling in a cluster based communications network 11 there isalso provided a cluster head device 12 a, 12 b a method performed by thecluster head device 12 a, 12 b, a computer program comprising code, forexample in the form of a computer program product, that when run on acluster head device 12 a, 12 b, causes the cluster head device 12 a, 12b to perform the method.

FIG. 2a schematically illustrates, in terms of a number of functionalmodules, the components of a wireless device 13 a, 13 b according to anembodiment. A processing unit 21 is provided using any combination ofone or more of a suitable central processing unit (CPU), multiprocessor,microcontroller, digital signal processor (DSP), application specificintegrated circuit (ASIC), field programmable gate arrays (FPGA) etc.,capable of executing software instructions stored in a computer programproduct 41 a (as in FIG. 4), e.g. in the form of a memory 23. Thus theprocessing unit 21 is thereby arranged to execute methods as hereindisclosed. The memory 23 may also comprise persistent storage, which,for example, can be any single one or combination of magnetic memory,optical memory, solid state memory or even remotely mounted memory. Thewireless device 13 a, 13 b may further comprise an input/output (I/O)interface 22 for receiving and providing information to a userinterface. The wireless device 13 a, 13 b also comprises one or moretransmitters 25 and receivers 24, comprising analogue and digitalcomponents and a suitable number of antennae 26 for radio communicationwith a network node 14, a cluster head device 12 a, 12 b, or anotherwireless device 13 b. The processing unit 21 controls the generaloperation of the wireless device 13 a, 13 b, e.g. by sending controlsignals to the transmitter 25 and/or receiver 24 and receiving reportsfrom the transmitter 25 and/or receiver 24 of its operation. Othercomponents, as well as the related functionality, of the wireless device13 a, 13 b are omitted in order not to obscure the concepts presentedherein.

FIG. 2b schematically illustrates, in terms of a number of functionalunits, the components of a wireless device 13 a, 13 b according to anembodiment. The wireless device 13 a, 13 b of FIG. 3 comprises a numberof functional units; a detecting unit 21 a and a reporting unit 21 b.The wireless device 13 a, 13 b of FIG. 2b may further comprises a numberof optional functional units, such as any of a performing unit 21 c, anda receiving unit 21 d. The functionality of each functional unit 21 a-dwill be further disclosed below in the context of which the functionalunits may be used. In general terms, each functional unit 21 a-e may beimplemented in hardware or in software. The processing unit 21 may thusbe arranged to from the memory 23 fetch instructions as provided by afunctional unit 21 a-d and to execute these instructions, therebyperforming any steps as will be disclosed hereinafter.

FIG. 3a schematically illustrates, in terms of a number of functionalmodules, the components of a cluster head device 12 a, 12 b according toan embodiment. A processing unit 31 is provided using any combination ofone or more of a suitable central processing unit (CPU), multiprocessor,microcontroller, digital signal processor (DSP), application specificintegrated circuit (ASIC), field programmable gate arrays (FPGA) etc.,capable of executing software instructions stored in a computer programproduct 41 b (as in FIG. 4), e.g. in the form of a memory 33. Thus theprocessing unit 31 is thereby arranged to execute methods as hereindisclosed. The memory 33 may also comprise persistent storage, which,for example, can be any single one or combination of magnetic memory,optical memory, solid state memory or even remotely mounted memory. Thecluster head device 12 a, 12 b may further comprise an input/output(I/O) interface 32 for receiving and providing information to a userinterface. The cluster head device 12 a, 12 b also comprises one or moretransmitters 35 and receivers 34, comprising analogue and digitalcomponents and a suitable number of antennae 36 for radio communicationwith a network node 14, a wireless device 12 a, 12 b, or another clusterhead device 13 b. The processing unit 31 controls the general operationof the cluster head device 13 a, 13 b, e.g. by sending control signalsto the transmitter 35 and/or receiver 34 and receiving reports from thetransmitter 35 and/or receiver 34 of its operation. Other components, aswell as the related functionality, of the cluster head device 12 a, 12 bare omitted in order not to obscure the concepts presented herein.

FIG. 3b schematically illustrates, in terms of a number of functionalunits, the components of a cluster head device 12 a, 12 b according toan embodiment. The cluster head device 12 a, 12 b of FIG. 3b comprises anumber of functional units; an acquiring unit 31 a and a determiningunit 31 b. The cluster head device 12 a, 12 b of FIG. 3b may furthercomprises a number of optional functional units, such as any of aperforming unit 31 c, a receiving unit 31 d, an adjusting unit 31 e, anda reporting unit 31 f. The functionality of each functional unit 31 a-fwill be further disclosed below in the context of which the functionalunits may be used. In general terms, each functional unit 31 a-b may beimplemented in hardware or in software. The processing unit 31 may thusbe arranged to from the memory 33 fetch instructions as provided by afunctional unit 31 a-f and to execute these instructions, therebyperforming any steps as will be disclosed hereinafter.

FIGS. 5 and 6 are flow charts illustrating embodiments of methods forcarrier frequency handling in a cluster based communications network asperformed by a wireless device 13 a, 13 b. FIGS. 7 and 8 are flow chartsillustrating embodiments of methods for carrier frequency handling in acluster based communications network as performed by a cluster headdevice 12 a, 12 b. The methods are advantageously provided as computerprograms 42 a, 42 b. FIG. 4 shows one example of a computer programproduct 41 a, 41 b comprising computer readable means 43. On thiscomputer readable means 43, at least one computer program 42 a, 42 b canbe stored, which at least one computer program 42 a, 42 b can cause theprocessing units 21, 31 and thereto operatively coupled entities anddevices, such as the memories 23, 33, the I/O interfaces 22, 32, thetransmitters 25, 35, the receivers 24, 34 and/or the antennae 26, 36 toexecute methods according to embodiments described herein. The computerprogram 42 a, 42 b and/or computer program product 41 a, 42 b may thusprovide means for performing any steps as herein disclosed.

In the example of FIG. 4, the at least one computer program product 41a, 41 b is illustrated as an optical disc, such as a CD (compact disc)or a DVD (digital versatile disc) or a Blu-Ray disc. The at least onecomputer program product 41 a, 41 b could also be embodied as a memory,such as a random access memory (RAM), a read-only memory (ROM), anerasable programmable read-only memory (EPROM), or an electricallyerasable programmable read-only memory (EEPROM) and more particularly asa non-volatile storage medium of a device in an external memory such asa USB (Universal Serial Bus) memory. Thus, while the at least onecomputer program 42 a, 42 b is here schematically shown as a track onthe depicted optical disk, the at least one computer program 42 a, 42 bcan be stored in any way which is suitable for the computer programproduct 41 a, 41 b.

First Overall Embodiment; Wireless Device

Reference is now made to FIG. 1 and FIG. 5. A method for carrierfrequency handling in a cluster based communications network 11 asperformed by a wireless device 13 b camping on or served by a clusterhead device 12 b associated with a cluster head carrier frequency f_(CH)will now be disclosed. An idle wireless device is camping on a clusterhead device 12 b (and hence is known by the cluster head device 12 b,but has no active connection to the cluster head device 12 b), whilst anactive wireless device is served by a cluster head device (and thus hasan active connection). Whether camping on or being served by a clusterhead device, the wireless device receives a downlink (DL) carrier on afirst reference carrier. The reference carrier frequency of the wirelessdevice may coincide with the carrier frequency of the cluster headdevice, but may differ somewhat due to Doppler shift and/or remainingfrequency error. Hence the status of the wireless device with respect tothe cluster head device is in-sync.

In general terms, the wireless device 13 b may receive measurementconfiguration message for the cluster head device 12 b indicatingprinciples for scanning for neighboring network nodes 14 and/or othercluster head devices 12 a. As will be further disclosed below, themeasurement configuration message may thus be either an intra-frequencymeasurement configuration message or an inter-frequency measurementconfiguration message. The wireless device 13 b thus scans for networknodes until a network node 14 is detected. It is assumed that a networknode 14 is detected. Hence, the processing unit 21 of the wirelessdevice 13 b is arranged to, in a step S102, detect a network node 14.The detecting may be performed by executing functionality of thedetecting unit 21 a. The computer program 42 a and/or computer programproduct 41 a may thus provide means for this determining. The networknode 14 is associated with a network node carrier frequency f_(NN).

If a NW node is detected the wireless device 13 b determines thefrequency difference between the network node 14 and the cluster headdevice 12 b the wireless device 13 b is operatively connected to. If thedifference is larger than a predetermined threshold Δ, a frequency errorevent is sent to the cluster head device 12 b. The processing unit 21 ofthe wireless device 13 b is thus arranged to, in a step S104 a, and in acase the cluster head carrier frequency differs more than apredetermined threshold Δ from the network node carrier frequency,report an event relating thereto to the cluster head device 12 b. Thereporting may be performed by executing functionality of the reportingunit 21 b. The computer program 42 a and/or computer program product 4ia may thus provide means for this reporting.

Reference is now made to FIG. 1 and FIG. 6. Embodiments relating tofurther details of carrier frequency handling as performed by a wirelessdevice 13 b camping on or served by a cluster head device 12 bassociated with a cluster head carrier frequency f_(CH) will now bedisclosed.

According to an embodiment the event comprises information of thedifference between the cluster head carrier frequency and the networknode carrier frequency. The event may be reported in an event report.Also other information may be included in the event report. For example,the processing unit 21 of the wireless device 13 b may be arranged to inthe event report also include network node information (such as, but notlimited to, cell ID, signal strength etc.).

Also in a case the difference is smaller than the predeterminedthreshold Δ say the wireless device 13 b may transmit a report to thecluster head device 12 b. For example, the wireless device 13 b mayreport network node information (such as, but not limited to, cell ID,signal strength etc.) to the cluster head device 12 b. According to anembodiment the processing unit 21 of the wireless device 13 b is thusarranged to, in an optional step S104 b, and in a case the difference issmaller than the predetermined threshold, report identity information ofthe network node to the cluster head device. The reporting may beperformed by executing functionality of the reporting unit 21 b. Thecomputer program 42 a and/or computer program product 4 ia may thusprovide means for this reporting

There may be different ways to detect the network node 14. According toan embodiment the processing unit 21 of the wireless device 13 b isarranged to, in an optional step S102 a, perform cell search so as todetect the network node 14. The cluster cell search may be performed byexecuting functionality of the performing unit 21C. The computer program42 a and/or computer program product 41 a may thus provide means forthis performing. This cell search may either be a regular cell searchwhere the wireless device 13 b searches for a regular network node 14 ora cluster cell search where the wireless device 13 b searches for afurther cluster head device 12 a inside the current cluster of thewireless device 13 b. Hence the network node 14 may be detected byperforming cell search within the cluster to which the wireless device13 b belongs as well as regular cell search for a network node 14outside the cluster to which the wireless device 13 b belongs. In theinter-frequency case the wireless device 13 b determines a network nodecarrier frequency on an inter-frequency carrier, and determines thefrequency difference to be larger than the predetermined threshold Δ, bycomparing the expected inter-frequency carrier (such as EARFCN; i.e.,the E-UTRA Absolute Radio Frequency Channel Number, where E-UTRA denotesEvolved Universal Terrestrial Radio Access) based on the cluster headdevice carrier frequency (i.e., where the EARFCN of the cluster headdevice 12 b is used), and the correct carrier frequency of the networknode 14 detected by the wireless device 12 b.

There may be different ways to acquire the predetermined threshold Δ.Different embodiments relating thereto will now be described in turn.For example, the predetermined threshold Δ may be hard coded from astandard of the communication protocol used. That is, according to anembodiment the predetermined threshold is determined according to acommunications standard or protocol. For example, the predeterminedthreshold Δ may be sent in a configuration message form the cluster headdevice 12 b the wireless device 13 b is operatively connected to. Thatis, according to an embodiment the processing unit 21 of the wirelessdevice 13 b is arranged to, in an optional step S102 b, receive thepredetermined threshold Δ from the cluster head device 13 b. Thereceiving may be performed by executing functionality of the receivingunit 21 d. The computer program 42 a and/or computer program product 41a may thus provide means for this receiving.

Second Overall Embodiment; Cluster Head Device

Reference is now made to FIG. 1 and FIG. 7. A method for carrierfrequency handling in a cluster based communications network 11 asperformed by a cluster head device 12 b associated with a cluster headcarrier frequency f_(CH) will now be disclosed.

The processing unit 31 of the cluster head device 12 b is arranged to,in a step S202, acquire a difference between the cluster head carrierfrequency and a network node carrier frequency f_(NN) associated with anetwork node 14. The acquiring may be performed by executingfunctionality of the acquiring unit 31 a. The computer program 42 band/or computer program product 41 b may thus provide means for thisacquiring. As will be further disclosed below there may be differentways to acquire the difference.

Based on the determined difference the cluster head device 12 b thendetermines how to handle the fact that the cluster head carrierfrequency deviates from the network node carrier frequency. Theprocessing unit 31 of the cluster head device 12 b is therefore arrangedto, in a step S204, determine, for a wireless device 13 b camping on orserved by the cluster head device, a frequency adjustment action out ofat least two possible frequency adjustment actions based on themagnitude of the frequency difference. The determining may be performedby executing functionality of the determining unit 31 b. The computerprogram 42 b and/or computer program product 41 b may thus provide meansfor this determining.

Reference is now made to FIG. 1 and FIG. 8. Embodiments relating tofurther details of carrier frequency handling as performed by a clusterhead device 12 b associated with a cluster head carrier frequency f_(CH)will now be disclosed.

There may be different ways to acquire the difference between thecluster head carrier frequency and the network node carrier frequencyf_(NN) associated with the network node 14. Different embodimentsrelating thereto will now be described in turn.

For example, the cluster head device 12 b may on a regular basis (suchas every 50-1000 ms) perform a scan for potential other cluster headdevices 12 a or network nodes 14 that may be in the vicinity of thecluster head device 12 b. The scanning may be similar to ordinary cellsearch. The processing unit 31 of the cluster head device 12 b may thendetermine, based on the outcome of the cell search whether a networknode 14 (or another cluster head device 12 a) is detected. According toan embodiment the processing unit 31 of the cluster head device 12 b isthus arranged to, in an optional step S202 a, perform a cell search andfrom the cell search detecting the network node so as to acquire thedifference. The cell search may be performed by executing functionalityof the performing unit 31 c. The computer program 42 b and/or computerprogram product 41 b may thus provide means for this performing.

For example, the cluster head device 12 b may receive a frequency error(frequency shift) event from a wireless device 13 b operativelyconnected to the cluster head device 12 b. According to an embodimentthe processing unit 31 of the cluster head device 12 b is thus arrangedto, in an optional step S202 b, receive an event report from thewireless device camping on or served by the cluster head device so as toacquire the difference. The receiving may be performed by executingfunctionality of the receiving unit 31 d. The computer program 42 band/or computer program product 41 b may thus provide means for thisreceiving. In such cases, the processing unit 31 of the cluster headdevice 12 b may determine the frequency shift needed in order to alignits carrier frequency with the network node carrier frequency asreported by the wireless device 13 b.

There may be different kinds of frequency adjustment actions to beperformed. The frequency adjustment actions may be performed byexecuting functionality of the adjusting unit 31 e. The computer program42 b and/or computer program product 41 b may thus provide means forthis adjusting. Different embodiments relating thereto will now bedescribed in turn.

One frequency adjustment action involves a step change which may beperformed at a specific time instant. According to an embodiment theprocessing unit 31 of the cluster head device 12 b is arranged toperform a first frequency adjustment action by, in an optional step S204c, determine a step change of the cluster head carrier frequency and atime instant for performing said change, wherein the step change isbased on said difference.

The frequency shift may also include a timing shift, i.e. the referencetiming may be needed to be changed in order to be aligned with thenetwork node timing. Therefore, the step change may be performed at atime instant occurring after operations such as, but not limited to,emptying potential data blocks in HARQ (Hybrid automatic repeat request)memories, etc.

One frequency adjustment action involves a gradual frequency adjustment.The rate of the gradual frequency adjustment may be slow, for example inthe order of 100-300 Hz/second, such that the internal AutomaticFrequency Controller (AFC) of the wireless device 13 b is able to followthe change. Thus, according to an embodiment the processing unit 31 ofthe duster head device 12 b is arranged to perform a second frequencyadjustment action by, in an optional step S204 d, gradually adjust thecluster head carrier frequency towards the network node carrierfrequency. The cluster head device 12 b may also explicitly inform thewireless device 13 b about the gradual frequency adjustment.

There may be different ways to determine which frequency adjustmentaction to perform. Different embodiments relating thereto will now bedescribed in turn.

For example, if the frequency difference is large (for example, in theorder of 2 kHz or more), the cluster head device 12 b may determine toperform the first frequency adjustment action (as in step S104 c) inorder to in a step align with the network carrier frequency. Accordingto an embodiment the processing unit 31 of the cluster head device 12 bis therefore arranged to, in an optional step S204 a, perform the firstfrequency adjustment action in a case said difference is larger than asecond predetermined threshold.

For example, if the frequency difference is small (for example, in theorder of 2 kHz or less), the cluster head device 12 b may determine toperform the second frequency adjustment action (as in step S104 d) inorder to gradually shift the carrier frequency towards the network nodecarrier frequency. According to an embodiment the processing unit 31 ofthe cluster head device 12 b is therefore arranged to, in an optionalstep S204 b, perform the second frequency adjustment action in a casethe difference is smaller than the second predetermined threshold.

The cluster head device 12 b may inform the wireless device 13 b aboutthe frequency change and potential timing change. According to anembodiment the processing unit 31 of the cluster head device 12 b isthus arranged to, in an optional step S206, report the determinedfrequency adjustment action to the wireless device camping on or servedby the cluster head device. The reporting may be performed by executingfunctionality of the reporting unit 31 f. The computer program 42 band/or computer program product 41 b may thus provide means for thisreporting.

There may be different ways for the cluster head device 12 b to informthe wireless device 13 b about the determined frequency adjustmentaction. Different embodiments relating thereto will now be described inturn.

The cluster head device 12 b may inform the wireless device 13 b aboutthe determined frequency adjustment action via dedicated signaling.Thus, according to an embodiment the processing unit 31 of the clusterhead device 12 b is arranged to, in an optional step S206 a, report thedetermined frequency adjustment action by transmitting dedicatedsignalling.

The cluster head device 12 b may inform the wireless device about thedetermined frequency adjustment action via broadcast messages. Thus,according to an embodiment the processing unit 31 of the cluster headdevice 12 b is arranged to, in an optional step S206 b, report thedetermined frequency adjustment action by transmitting a broadcastsignal.

In summary there has been presented embodiments relating to carrierfrequency handling in a cluster based communications network 11.

In a first overall embodiment, a wireless device operatively connectedto a cluster head device has been disclosed. A wireless device 13 b in acluster outside network coverage scans for network nodes and detects anetwork node 14. The wireless device 13 determines a frequencydifference between the cluster head device 12 b and the network node 14.If the difference is larger than a predetermined threshold it reports afrequency event to the cluster head device 12 b. In one embodiment thepredetermined threshold is determined from a communication standard, andin another embodiment it is based on configuration information receivedfrom the cluster head device 12 b.

In a second overall embodiment a cluster head device 12 b determines aneed for adjusting a carrier frequency used for communications with awireless device 13 b in the cluster served by the cluster head device 12b. The adjustment is needed in order for the carrier frequency to bealigned with a network node 14 with a better clock accuracy than theclock accuracy of the cluster head device 12 b. In some embodiments, thecluster head device 12 b itself determines the need, and in otherembodiments the cluster head device 12 b receives an event form awireless device 13 b in the cluster. In further embodiments theadjustment is accomplished by a frequency shift and wireless devices 13b in the cluster are informed, via broadcast message or dedicatedsignaling. In other embodiments the cluster head device 12 b graduallyadjusts the carrier frequency towards the network node carrierfrequency. Also in this embodiment the wireless devices 13 b in thecluster may be informed.

However, as is readily appreciated by a person skilled in the art, otherembodiments than the ones disclosed above are equally possible withinthe scope of the inventive concept, as defined by the appended patentclaims. For example, the wireless device may be scanning not only fornetwork nodes 14, but also for other cluster head devices outsidenetwork coverage.

The skilled person further understands that, although the disclosedsubject matter is described in a LTE context and the clusters have beendescribed in a NSPS scenario, the enclosed embodiments are neitherlimited to LTE, nor to cluster head devices being the type of wirelessdevices as described above. The enclosed embodiments cover any kind oflow power network node controlling other nodes or devices, with someinaccurate clock reference compared to another (network) node havingbetter clock (and carrier frequency) accuracy.

1-6. (canceled)
 7. A method for carrier frequency handling in a clusterbased communications network, the method comprising: a cluster headdevice associated with a cluster head carrier frequency performing:acquiring a difference between the cluster head carrier frequency and anetwork node carrier frequency associated with a network node; anddetermining, for a wireless device camping on or served by the clusterhead device, a frequency adjustment action out of at least two possiblefrequency adjustment actions based on the magnitude of the frequencydifference.
 8. The method according to claim 7, further comprising:performing a cell search and from the cell search detecting the networknode so as to acquire the difference.
 9. The method according to claim7, further comprising: receiving an event report from the wirelessdevice camping on or served by the cluster head device so as to acquirethe difference.
 10. The method according to claim 7, wherein a firstfrequency adjustment action comprises: determining a step change of thecluster head carrier frequency and a time instant for performing saidchange, wherein the step change is based on said difference.
 11. Themethod according to claim 7, wherein a second frequency adjustmentaction comprises: gradually adjusting the cluster head carrier frequencytowards the network node carrier frequency.
 12. (canceled)
 13. Themethod according to claim 11, further comprising: performing the secondfrequency adjustment action in a case said difference is smaller than asecond predetermined threshold.
 14. The method according to claim 7,further comprising: reporting said determined frequency adjustmentaction to the wireless device camping on or served by the cluster headdevice.
 15. The method according to claim 14, further comprising:reporting said determined frequency adjustment action by transmittingdedicated signalling.
 16. The method according to claim 14, furthercomprising: reporting said determined frequency adjustment action bytransmitting a broadcast signal.
 17. (canceled)
 18. A cluster headdevice for carrier frequency handling in a cluster based communicationsnetwork, the cluster head device being associated with a cluster headcarrier frequency, the cluster head device comprising a processing unitarranged to: acquire a difference between the cluster head carrierfrequency and a network node carrier frequency associated with a networknode; and determine, for a wireless device camping on or served by thecluster head device, a frequency adjustment action out of at least twopossible frequency adjustment actions based on the magnitude of thefrequency difference.
 19. (canceled)
 20. A nontransitory computerreadable storage medium comprising a computer program for carrierfrequency handling in a cluster based communications network, thecomputer program comprising computer program code which, when run on acluster head device associated with a cluster head carrier frequency,causes the cluster head device to: acquire a difference between thecluster head carrier frequency and a network node carrier frequencyassociated with a network node; and determine, for a wireless devicecamping on or served by the cluster head device, a frequency adjustmentaction out of at least two possible frequency adjustment actions basedon the magnitude of the frequency difference.
 21. (canceled)